According to an image forming apparatus that forms an image electrophotographically, the image is formed on a sheet and the image is then heat-fixed on the sheet by a fixing device. It has been known that the sheet is shrunken upon the heat fixing.
There has been disclosed a technology of coping with the shrinkage of the sheet. For example, there has been disclosed a technology of adjusting a positional deviation between a surface and a backside upon a duplex printing. In this technology, an image forming apparatus is configured to first form a mark for adjustment on one surface of a sheet. Then, the mark is measured by a sensor before the sheet passes through a fixing device. After that, the sheet having the mark formed thereon is enabled to pass through the fixing device, the sheet is conveyed to a measurement position of the same sensor without reversing the surface and backside of the sheet, and the mark is measured by the sensor. Then, a sheet shrinkage ratio is specified from the first measurement result and the second time measurement result.